Automated cutting of synthetic gemstones

Abstract

A computer implemented / automated method of cutting a synthetic rough gemstone in to at least one target gemstones, involves (i) the provision of a synthetic rough gemstone, (ii) obtaining at least o

Description

Technical Field The inventive concept relates to the cutting of synthetic rough, or as-grown, gemstones. In particular, the inventive concept relates to the cutting of synthetic rough diamonds. Background A conventional process for extracting one or more cut and polished gemstones from a rough natural stone typically comprises many stages. The first is the scanning stage, in which a 3D model of a rough stone is created from scans which determine its (often unique) shape, and note the location of any defects or non-gemstone material, known as inclusions. Next comes the planning stage, in which the shape and size of the target gemstone(s) to be cut from the rough stone is determined, based upon maximising the output from the stone, whilst minimising waste. The shape and size of the gemstone(s) to be cut from the rough stone may also be determined based upon the clarity and colour of the rough stone. During the cutting stage, the target gemstone(s) is cut from the rough gemstone using a laser. Finally, polishing is employed to complete the cut and polished natural gemstone. Figure 1 illustrates a conventional 3D model produced in the scanning stage and used to plan the target gemstone(s). Based upon one or more scans, software (such as Advisor® rough stone planning software, DiaExpert® rough diamond modelling platform and the Diamark® marking system by Sarine Technologies Ltd) generates a 3D model 10 of the rough stone 20. The 3D model 10 also indicates the location of one or more cut gemstones 30 (target gemstones) to be cut from the rough stone 20, avoiding any cracks, faults, or inclusions. Based upon the 3D model, the specific cut and final shape may be selected, or planned, by an experienced operator in order to extract the highest value of polished gemstone 30 within the rough stone 20. The model of the target gemstone generated by the planning software is typically produced in a suitable file format. In order to provide instructions for the cutting stage to a Computer Numerical Control (CNC) machine, the file(s) must be converted to G- code, a CNC programming language. Use of G-code enables a multi-axis CNC machine with a laser, such as a neodymium YAG laser, to iteratively cut a rough gemstone into a programmed, precise, multi-facetted shape. The heat of the laser can leave black graphitic marks, which will need to be subsequently removed, and the need to remove these graphitic marks must be taken into account during the planning. Typically, following the cutting stage, the cut stone will not have as many facets as the final desired stone. For example, the initial cutting process may result in 16 facets (8 at the bottom and 8 at the top), or a coned shape. As a result, the cut gemstone must then be polished by one or more skilled polishers to create the final number of smooth facets. In summary, the process of scanning, planning, cutting and polishing a rough natural stone into a final cut and polished gemstone is labour intensive, time consuming and difficult to optimize. Summary In one aspect of the present invention, there is provided a computer implemented method of cutting a synthetic rough gemstone into one or more target cut gemstones. The method comprises providing a synthetic rough gemstone comprising usable and unusable gemstone material; obtaining one or more physical parameters of the synthetic rough gemstone; determining an extent of the usable gemstone material; defining one or more target gemstones to be cut from the usable gemstone material; calculating an optimal fit of the one or more target gemstones into the usable gemstone material; and generating computer readable instructions for cutting the one or more target gemstones from the synthetic rough gemstone. The method may comprise allocating the one or more physical parameters of the synthetic rough gemstone into one of a plurality of predetermined ranges, and defining the one or more target gemstones based upon the allocated range. Calculating the optimal fit may comprise determining a main cutting plane, wherein the main cutting plane is defined by the computer readable instructions as the first cut through the synthetic rough diamond during the cutting process, and wherein the main cutting plane defines one of the facets of one or more of the target gemstones. The method may comprise building subsequent cuts from the main cutting plane. The method may comprise cutting the one or more target gemstones from the synthetic rough gemstone using a laser, preferably a dry laser, based upon the computer readable instructions. The one or more physical parameters may comprise one or more of: height, growth face area, offset, height, single crystal volume. The defining one or more target gemstones may comprise generating a 3D mesh model based upon the one or more physical parameters. The cutting may be carried out within a coordinate system of the synthetic rough gemstone. The method may comprise polishing the one or more target gemstones to remove carbonisation. The computer readable instructions may comprise a cutting order of facets of the one or more target gemstones. The method may comprise determining the cutting order of facets to minimise a time required to cut the one or more target gemstones from the rough gemstone. The method may comprise determining the cutting order to optimise a number of target gemstones cut from the rough gemstone. The method may comprise determining points of intersection between facet planes of the one or more target gemstones and the rough synthetic gemstone. The method may comprise mounting the synthetic rough stone on a mount; adjusting relative positions of the mount and the synthetic rough stone such that a position of the defined one or more target gemstones relative to the mount is known. The method may comprise illuminating and imaging the synthetic rough gemstone through a surface of the synthetic rough gemstone that is substantially free from unusable material to obtain the one or more physical parameters of the synthetic rough gemstone. The synthetic rough gemstone may be a diamond, and the usable gemstone material may be single crystal diamond and the unusable gemstone material may be polycrystalline diamond, PCD. In a further aspect there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of the first aspect above. In another aspect, there is provided a data processing apparatus comprising a processor and configured to perform the method of the first aspect above. Brief Description of Drawings Figure 1 illustrates a conventional three-dimensional model of a natural rough gemstone; Figure 2 illustrates a synthetic diamond with polycrystalline diamond (PCD) skin; Figures 3a, 3b and 3c illustrate various lighting conditions; Figure 4 illustrates measurement of a physical parameter of a synthetic gemstone; Figures 5a and 5b illustrate methods of cutting a synthetic gemstone; Figure 6 illustrates a side view of a synthetic gemstone; Figure 7 illustrates a plan view of a synthetic gemstone mounted on a dop; and Figure 8 illustrates a method of cutting a synthetic (lab-grown) gemstone into one or more target stones. Description While the following description refers in particular to synthetic diamonds, it will be appreciated that the inventive method and associated apparatus may also be applied to other types of synthetic (e.g. lab-grown) gemstones. Synthetic gemstones (e.g. lab-grown gemstones), such as those formed by Chemical Vapor Deposition (CVD), differ from natural gemstones in that they generally do not comprise inclusions because they grow much more quickly than natural stones, which are formed very slowly in the earth’s crust. Additionally, the colour and clarity of synthetic stones can be closely controlled. Synthetic gemstones such as diamond can be grown using a “seed” stone mounted in the centre of a dop (or other type of mount) within a vacuum chamber. The chamber is filled with carbon- and hydrogen-heavy gases and heated to a very high temperature, turning the gases into plasma, and the crystal then grows on the seed. As illustrated in Figure 2, stones such as CVD diamonds 100 are usually formed with a black edge or skin of polycrystalline diamond (PCD) 120 around the sides of the single crystal diamond material 140. Because of the nature of the growth process, this skin does not form on the top or the bottom of the grown diamond. This PCD skin, or rim, must be removed as part of the process which transforms a rough synthetic diamond into one or more cut and faceted gemstone diamonds. The inventors have realised it is possible to take advantage of the differences between natural and synthetic stones to produce a method of cutting and shaping synthetic gemstones which is simpler and faster than the traditional methods associated with natural gemstones described above. Using the inventive method described herein, no 3D model of the stone is necessary, no planning is required, and no additional facets need to be introduced via post-cutting polishing. Instead, the target stone (in other words, the one or more stones to be cut from the rough material) is determined by the size of the starting material and the desired shape of the target gemstone. The inventive method, steps of which are implemented by a computer, provides a synthetic gemstone cutting process that can be carried out in any geographical location, with any laser, and which can take the form of a single process, thereby replacing the multiple processes required by traditional methods associated with natural gemstones. In particular, any post-cutting polishing steps need only follow the facets already cut by the laser, and no decision-making around polishing locations or additional facet creation is required. In theory, the overall manufacturing process could be reduced dramatically, and in some circumstances to around four hours. Rough synthetic diamonds ( / .e. as-grown diamonds) grown according to a specific process typically have a repeatable geometric shape. In the following description, the term “rough” refers to the as-grown synthetic (man-made) diamond prior to cutting. One or more physical parameters, or one or more measurements, of the rough synthetic diamond, as grown, are obtained post-growth and prior to cutting. The parameters of interest may include one or more of: height, growth-face perimeter, rotational and axial displacement between the seed and the growth face. In an example, one or more physical parameters of the rough synthetic stone are obtained by scanning or imaging the stone through the growth-face, which is generally an upper (or top) surface of the stone. As discussed above, for diamonds grown by CVD, PCD material does not generally form on the top surface (growth face) of the stone. In other words, the surface furthest away from the original seed (or the location thereof where the seed is no longer present) is substantially free from PCD material, and is therefore substantially transparent and can be used as a window into the interior of the single crystal diamond material. An apparatus for obtaining the one or more physical parameters of the rough synthetic stone may comprise a mount, such as a dop, for mounting the stone; and one or more imaging or scanning devices configured to capture one or more images or scans of the stone. The apparatus may further comprise a processor configured to extract or otherwise calculate the one or more physical parameters of the rough synthetic stone from the captured one or more images or scans. The purpose of the scanning or imaging is to determine the extent of the single crystal diamond material within the rough stone, and the interfaces between the single crystal diamond material and the PCD material. Thus, the entire rough stone, including single diamond crystal and PCD, may be scanned and / or imaged. The boundaries of the single crystal diamond (i.e. the points at which single crystal diamond material meets the PCD material) can be determined from the scans or images. In one example, the rough synthetic stone is scanned and / or imaged under a set of specific lighting conditions. These conditions may include one or more of: flat, diffuse lighting, in which the stone is illuminated through a window (e.g. the growth face) from above a plane in which the window lies, as shown in Figure 3a; “dome” or multidirectional bright field lighting, as shown in Figure 3b; and dark field lighting, in which the stone is illuminated at an angle from the window plane and imaged from above as shown in Figure 3c. However, the inventive concept is not limited to these lighting conditions, and other suitable lighting conditions, or combinations of lighting conditions, may be used. In this case, the above-mentioned apparatus would therefore further comprise one or more suitable light sources, together with associated lenses, filters and the like, accordingly. In one non-limiting example, the rough stone is mounted, optionally using the mount on which the stone was grown, and rotated so that multiple images of an interior of the stone and / or an exterior of the stone may be obtained by one or more imaging devices and combined using a processor. For example, around twenty-four images of the interior and / or exterior of a rough stone may be obtained at different rotational positions of the stone. In this case, the above-mentioned apparatus would further comprise a rotation device configured to rotate one or both of the mount and the one or more imaging devices. The rotation device may optional comprise a stepper motor. Unlike the planning process used for a natural rough diamond, discussed above, it is not necessary to create a 3D model of the synthetic rough stone from any images obtained. Instead, the target diamond(s) (the diamond or diamonds to be cut from the original rough stone) can be determined based simply upon the one or more physical parameters obtained by the scanning and / or imaging of the rough stone, including the usable single diamond crystal material and the unusable PCD material. In one example, the one or more measured physical parameters include one or more of: the area of the single crystal growth rectangle or face (essentially the top surface or growth face of the as-grown stone, excluding PCD material) and the height of the stone. Measured physical parameters may also include: the stone’s offset (the axis shift between the centre of the seed from which the stone is grown and the centre of the top square / top surface of the stone, excluding PCD material); the stone’s twist (the rotation between the XY axis of the seed and the top growth face of the stone, excluding PCD material). Other characteristics of the stone may be known from the specific growth conditions, or may be measured. It will be appreciated that one or more of these physical parameters may be selected alone or in combination. Figure 4 illustrates one method of measuring a stone’s offset and or twist. The stone 100 appears in plan view, with the top growth plane (or window) of the single crystal diamond material 140 enabling a view down onto the original diamond seed 160. The usable diamond material 140 is surrounded by an edge or skin of PCD material 120. A cross + marks the centre of the growth plane CG, while an x marks the centre of the seed CS. The difference in coordinates of the two centres CG and CS will define the offset (the axis shift between the centre of the seed and the centre of the top growth face) and also any twist (the rotation between the XY axis of the seed and the top growth face of the stone). The measured physical parameters of the stone determine the single crystal volume, i.e. the volume of single diamond crystal material present, excluding PCD material. The single crystal volume represents the usable volume of the stone. The single crystal volume can of course be considered as another measured physical parameter of the stone. A small number of ranges, or sub-sets, corresponding to single crystal volumes or other measured physical parameters, are provided, such that for each range or subset, a designated number and location of target stones are cut from the rough single crystal diamond material. Said another way, for each rough stone, the measured single crystal volume or other measured parameter will fall within one of the ranges, or clusters. The inventive method and apparatus may therefore take advantage of the growth patterns of synthetic stones, wherein stones grown according to a particular process and / or in a particular batch tend to have similar singe crystal volumes, even though the PCD material may vary. For each specific predetermined range of single crystal volume, or other measured parameter, the same output stone(s) will be cut using the same set (or sets) of preprepared cutting instructions. This approach greatly simplifies the “planning” of the target gemstone, since rough stones which fall within the same predetermined range (in terms of the volume of usable single crystal diamond material, or other measured parameter) will be cut to produce substantially identical output stones. It will be appreciated that the provision of a small number of predetermined ranges, each associated with a specific set of pre-prepared cutting instructions, can be used to automate the cutting of rough stones, since, once the physical parameters of a stone have been obtained, the stone can be automatically assigned to a specific range and cut accordingly. The pre-prepared ranges may of course be determined so as to minimise waste of single crystal diamond material. For example, the ranges may be determined such that each range encompasses only small variations in physical parameters. Typically, a rough synthetic diamond material is cut into more than one target gemstone. For example, a single rough synthetic stone may be cut into four or more target stones. These target stones may be the same or different sizes. However, it will be appreciated that the method and apparatus described herein could be used to cut a single target gemstone from the rough material. Thus, the inventive method avoids the requirements to obtain sophisticated 3D models of a rough gemstone. Instead, once the one or more physical parameters of the rough stone have been obtained, the rough material will be automatically cut according to a set (or sets) of pre-determined cutting instructions, depending on which pre-set range it falls within, and optionally the specific shape (and / or number of stones) required. It will be appreciated that, although predetermined ranges are used to allocate one or more target stones to be cut from a particular rough stones, cutting instructions for the laser may need to be adjusted to accommodate the specific physical characteristics of the particular rough stone, as previously measured. In one non-limiting example, the generation of cutting instructions for the laser, according to the inventive method, is accomplished as follows. A processor, implemented by hardware and / or software and connected directly or indirectly to a memory, runs software comprising algorithms which transform cutting instructions derived from the one or more measured physical parameters of the rough stone (such as the single crystal volume) into a language that the laser understands. In one non-limiting example, the software generates a LUF file (a proprietary file of Bettonville™) which can then be further converted into G-code, or another appropriate format, by a post processor (for example, at the laser apparatus) to create a laserpath. The processor may form part of the above-mentioned apparatus, but may also form part of a separate device or system. In one example, the process begins by defining a 3D mesh file, comprising vertices and corners of the desired target stone(s), which can also be referred to as a mathematical model of the target stone(s). In this example, the model is a predetermined target mesh model (e.g. an STL or X file)selected (optionally from a database of models) based upon the one or more input physical parameters of the specific rough stone (for example, the rough’s stone’s height, growth face area, single crystal volume) and the predetermined range into which the rough stone falls. The selection is made such that the target stone(s) is “fitted” within the rough stone in a way which optimises the yield from the usable material of the rough stone. As discussed above, the single crystal diamond material of the rough stone can be considered as the usable rough material, while the PCD skin or outer layer is the unusable material. This target mesh model is a result of target proportions (facet angles etc.) and may depend upon the specific cut required (for example, whether the cut is required to be EX (Excellent) or VG (Very Good) etc). In this example, the target models are preprepared, but in other examples the target models could be generated as required. Continuing this example, the afore-mentioned algorithms then work to simplify the 3D mesh file, by finding the mesh facet edges; allocating lines and vertices of rough and target meshes; converting perimeters to triangles, and simplifying triangles to reduce the total number (there are many triangles on a facet plane, only one or two will be stored in memory). It will be appreciated that the order of these steps may vary and that steps may be repeated or omitted as required. Images of the rough and target stone(s) can be sent, if required, to a graphical user interface (GUI), which in one example is a 3D viewer in Visual Basic. Optionally, the GUI may display a computer aided design (CAD) model of the stone at the GUI, for example, for confirmation purposes. In this example, the algorithms then fill in the "facet structure" for all the facets of the target stone(s). Facets are grouped by type (e.g. tiers: pavilion, lower girdle, bezel, upper girdle, star). Geometrical information (for example, area, highest point, length, normal etc.) is computed by the processor and stored in the memory. An equation for each plane is calculated (for example, ax+by+cz+d=0) and the coefficients of this equation are stored in the memory. Continuing with this example, each plane of the target gemstone(s) is intersected with the rough stone, based upon the measured physical parameters, to “trim” the plane. Points of intersection between the desired target stone(s) and the actual rough stone are stored in the memory. The equation for the line of cutting, or stroke line (the line which the laser will use to cut a particular facet), is computed, as illustrated in Figure 5a. In the specific example shown in Figure 5a, the target stroke segment is AB (the cut creating the facet on the target stone, T), the rough stroke segment is CD (the cut through rough material, R), the lead in is EC (the line taken by the laser before cutting starts) and the lead out is DF (the line taken by the laser after cutting ends). This stroke line of ABCDEF points is transformed by the processor into a LUF file, or other file type. Stoke line ABCDEF may be the first cut made by the laser and, where more than one target gemstone T is to be cut from the rough stone R, stroke line ABCDEF may form a facet of more than one stone. In this example, stroke ABCDEF represents a main cutting plane, from which subsequent cuts are built. This is of course one example of a stroke line, and the invention is not limited thereto. Once complete cutting instructions have been generated, the file is sent to the laser cutting machine, for example via a physical or wireless connection, or can of course be manually inputted into the laser cutter. It will be appreciated from the above that calculation of the strokes ABCDEF is carried out with reference to the coordinate system of the stone (the workpiece co-ordinate system WCS), not the laser cutting machine (machine coordinate system MCS), although of course the machine itself will work in MCS. As previously discussed, lab-grown diamonds (e.g. CVD stones) are formed with a black external layer or skin of polycrystalline diamond (PCD). Additionally, the heat of the laser during cutting can leave graphitic black marks or layers. In both cases, unusable material is formed. To accommodate this layer or skin of unusable material, the mathematical model of the target stone is modified to include an additional layer or envelope ENV around the target stone(s) T, as illustrated in Figure 5b. In one example, this additional layer has a thickness of around 20 microns, sufficient to protect the boundaries of the target stone(s) and to accommodate any PCD and / or heat marks. Therefore, the model of the target gemstone comprises a definition of an interface between usable and unusable material in the rough stone. Once cutting is complete, any remaining unusable layer or skin, such the carbonisation created by the laser, is polished off the target gemstone. It will be appreciated that removal of the non-usable graphitised skin by polishing is accomplished by simply following the facets introduced by the laser cutter, and that no additional facets are introduced during the polishing process. Since all required facets of the target stone(s) are produced during the cutting step, polishing time is drastically reduced compared with the traditional methods associated with natural gemstones. The algorithms or logic operated by the processor (implemented as software and / or hardware) also compute an optimised cutting order for the facets of the target stone(s). Optimisation can include changing the cutting order to “promote” one or more facets so that the promoted facets are cut before others. In one example, optimisation of the cutting order is carried out so as to reduce the overall cutting time. For example, the first cut can be selected so that the second cut is shortened. In one example, optimisation of the cutting order takes into account the position of the facet in the target stone(s). For example, as illustrated in Figure 6, cutting must be carried out very accurately at the points marked X, in the position of the girdle of the target stone T, where a corner or vertex of the target stone is very close to the outer edge of the rough stone R. In other positions, such as where a facet of the target stone T is further from the outer edge of the rough stone R, cutting can be completed more quickly as accuracy is not so important. Although Figure 6 illustrates a single target stone, as discussed above, multiple target stones may be cut from a single rough synthetic stone. In one example, cutting may be carried out to split the original rough diamond material into multiple stones, which are then individually re-mounted separately and further laser cut to provide the desired number of facets. It will be appreciated that each of these stones may comprise a layer of PCD material. An example process of how a rough gemstone may be mounted in order to be laser cut into a target stone or stones will now be described. The rough gemstone is mounted on a dop (or other type of mount) to micron accuracy. A small amount of adhesive may be used to fix the rough stone to the dop. The dop itself is mounted to a machine stage. In one example, where the dop or mount is metallic, the machine stage is a magnet. Continuing the above example, both the mount and the rough stone are set in a known location with respect to the laser cutter. This known location may be an externally marked reference point. To enable the rough stone to be accurately mounted so that a centre of the target stone (for example, the largest target stone, where more than one stone is to be cut) is located in a centre of the dop, the following process is followed. This process enables a position of the target stone relative to the dop to be known. With reference to Figure 7, the mounted stone R and dop DOP are imaged (e.g. along an axis parallel with a longitudinal axis of the dop, for example, through the growth surface). This imaging may take place at the same time as the physical parameters of the stone are measured, and the coordinate system and origin may then be passed to the laser system. A circle GRD is drawn or otherwise superimposed upon the image, the circle GRD representing a girdle of the target stone. The girdle is defined as the widest point of the target stone, and the position at which the bottom of the crown meets the top of the pavilion. The before-mentioned circle may be provided by the laser cutting apparatus as a preview of the laser path. From the image, two measurements are obtained: measurement L1, which is a distance between an uppermost point (in plan view) on the perimeter of the circle GRD and the uppermost outer edge of the dop DOP; and measurement L2, which is a distance between a lowermost point (in plan view) of the perimeter of the circle GRD and the corresponding lower outer edge of the dop DOP. If measurements L1 and L2 when measured are the same, then the circle GRD representing the girdle of the target stone is in centre of the dop DOP, and the relationship between the target stone and the dop is known. However, if L1 is greater than L2, or if L2 is greater than L1, then the stone is skewed and dop must be moved in relation to the rough stone. As discussed above, when determining the size of the girdle of the target stone, a cutting allowance is added to the envelope of the target stone. In this example, measurements L1 and L2 are obtained by obtaining one or more images of the stone and dop, for example using a camera, magnifying the one or more images and then obtaining the measurements from the magnified images. It will be appreciated that other methods of obtaining measurements L1 and L2, or other measurements or methods which verify the central (or otherwise) location of the target stone relative to the dop can be used. In one example, small movements or adjustments of the dop are carried out in an automated manner, but movement of the dop can also be carried out manually. These small adjustments of the dop relative to the rough stone assist in avoiding the traditional step of modelling the rough stone and planning the location of the target stone within the rough stone. In one, non-limiting example, the dop moves automatically with an axis of a laser cutting machine (following LUF instructions). When the dop is first set into the machine, it is referenced by pushing the dop so that the dop moves on the magnet of the machine and it basically changes its origin, or reference point, so that this is known. It will be appreciated that, since synthetic diamonds are grown from seeds, at some stage in the cutting process the seed, where still attached to the rough stone, will be removed by cutting. In one example, and with reference to Figure 8, the inventive method of cutting a synthetic rough gemstone into one or more target cut gemstones therefore comprises the steps of: S1: providing a synthetic rough gemstone comprising usable and unusable gemstone material; S2: obtaining one or more physical parameters of the synthetic rough gemstone; S3: determining an extent of the usable gemstone material; S4: defining one or more target gemstones to be cut from the usable gemstone material; S5: calculating an optimal fit of the one or more target gemstones into the usable gemstone material; and S6: generating computer readable instructions for cutting the one or more target gemstones from the synthetic rough gemstone. It will be appreciated that the above steps may be carried out in a different order, and that steps may be omitted or replicated, and further steps not included above may be added, without departing from the scope of the inventive concept. As described herein, the target gemstone may comprise a cut and faceted stone formed from usable gemstone material. This usable material is single crystal diamond material. It will be appreciated that the target gemstone may include one or more layers of carbonised material which are removed by polishing. It will be appreciated that the inventive concepts described above are examples which may be varied and / or combined without limitation, and that the scope of protection is defined only by the claims which follow.

Claims

1. A computer implemented method of cutting a synthetic rough gemstone into one or more target cut gemstones, the method comprising:providing a synthetic rough gemstone comprising usable and unusable gemstone material;obtaining one or more physical parameters of the synthetic rough gemstone; determining an extent of the usable gemstone material;defining one or more target gemstones to be cut from the usable gemstone material;calculating an optimal fit of the one or more target gemstones into the usable gemstone material; andgenerating computer readable instructions for cutting the one or more target gemstones from the synthetic rough gemstone.

2. The method according to claim 1, further comprising allocating the one or more physical parameters of the synthetic rough gemstone into one of a plurality of predetermined ranges, and defining the one or more target gemstones based upon the allocated range.

3. The method of claim 1 or 2, wherein calculating the optimal fit comprises determining a main cutting plane, wherein the main cutting plane is defined by the computer readable instructions as the first cut through the synthetic rough diamond during the cutting process, and wherein the main cutting plane defines one of the facets of one or more of the target gemstones.

4. The method of claim 3, further comprising building subsequent cuts from the main cutting plane.

5. The method according to any preceding claim, further comprising cutting the one or more target gemstones from the synthetic rough gemstone using a laser, preferably a dry laser, based upon the computer readable instructions.

6. The method according to any preceding claim, wherein the one or more physical parameters comprise one or more of: height, growth face area, offset, twist, single crystal volume.

7. The method according to any preceding claim, wherein the defining one or more target gemstones comprises generating a 3D mesh model based upon the one or more physical parameters.

8. The method according to any preceding claim, wherein the cutting is carried out within a coordinate system of the synthetic rough gemstone.

9. The method according to any preceding claim, further comprising polishing the one or more target gemstones to remove carbonisation.

10. The method according to any preceding claim, wherein the computer readable instructions comprise a cutting order of facets of the one or more target gemstones.

11. The method according to claim 10, further comprising determining the cutting order of facets to minimise a time required to cut the one or more target gemstones from the rough gemstone.

12. The method according to claim 10 or 11, further comprising determining the cutting order to optimise a number of target gemstones cut from the rough gemstone.

13. The method according to any preceding claim, further comprising determining points of intersection between facet planes of the one or more target gemstones and the rough synthetic gemstone.

14. The method according to any preceding claim, further comprising: mounting the synthetic rough stone on a mount;adjusting relative positions of the mount and the synthetic rough stone such that a position of the defined one or more target gemstones relative to the mount is known.

15. The method according to any preceding claim, further comprising illuminating and imaging the synthetic rough gemstone through a surface of the synthetic roughgemstone that is substantially free from unusable material to obtain the one or more physical parameters of the synthetic rough gemstone.

16. The method according to any preceding claims, wherein the synthetic rough 5 gemstone is a diamond, and wherein the usable gemstone material is single crystal diamond and the unusable gemstone material is polycrystalline diamond, PCD.

17. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of claims 1 to 16.

018. A data processing apparatus comprising a processor configured to perform the method of claims 1 to 16.19

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